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Hg 2879c

Discussion in 'Amplifiers' started by Skydiver256, Mar 24, 2021.

  1. Shockwave

    Shockwave Sr. Member

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    So much for spending the extra money on "matched" HG transistors. Did you happen to test the hfe of them before installation to see if they were even close on DC gain? Not that this will tell you how they respond at RF, but it would be interesting to see if they are even making any effort to match at DC. If you can't see a difference at DC, start checking the base to emitter capacitance and the collector to emitter capacitance. This will likely reveal why the input and output impedances are different at RF. You can probably do a better job of matching them, than what you paid for.

    My mind is still shocked that no one has cracked open the back of a modern mobile HF rig and started cloning the two transistor RD100HFF1 output stage, as opposed to struggling with these parts that are simply not as advertised. If I still had a 12 volt "customer base", this would have been the very first thing to do. Imagine the advantage you would have, using the latest and most advanced RF output MOSFET's, in the 12 volt class? While not the way to go for base use, until our vehicles start using 48 volt electrical systems, the RD100HFF1 is the only HF, 12 volt, 100 watt, linear RF transistor in production today, that is worth working with.


     

  2. Crusher

    Crusher Well-Known Member

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    These were matched by curve tracer, marked 63, I used Sencore TF46 and did check hfe. I went through 18 to find 6 that tested 41 & 42. Yes I used power device setting not small signal setting.

    I have built a few 2 device using the rd100fhh1 device. I like it. But still not really for a CB’er. As more drive is better mentality will kill them too. One I have now I still have a little more to do as it’s showing a oscillation on the spectrum analyzer. Think I need more DC filtering.
     
  3. flush

    flush Member

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    I have new real 2879As. How do I sell them since there's so many fakes out there.
     
  4. Dr_DX

    Dr_DX Well-Known Member

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  5. Tokin

    Tokin The Man With No Shoes

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    Thats a BBI quote lol.
    HG is all there is and most builders are making them work, texas star being the only exception i know of who are using supposed dei which i believe are restamped older versions of hg's. I wouldnt be surprised if the famous 6-j toshiba fakes are an older restamped hg version.
    I dont hear of users bitching about C's or the 16d08 as long as swr, drive and volts are kept to moderate levels. FatBoy is selling a lot of hg amps as is carl built, hopper and others. Rooster radio on yt has been getting monthly shipments from fatboy and selling out. The last i saw was a 16 pill 2879C amp 400 amp regulated supply combo ( ) and a crap load of 4 and 8 pill amps. Give it a year and see how many of these amps have issues. Till then ill keep buying toshiba amps that come up for sale locally. Lots of older operators
    Gatekeeper still has my dx1600 rebuild with 2879C's in line to be worked on. Im interested to see how it performs. Thanks to some radio family ive got a couple good toshiba amps to run till I get the hg.
     
  6. Dmans

    Dmans Sr. Member

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    Tokin,
    Good to see you back on the Forum. Don't stay gone so long next time!

    73
    David
     
    Shadetree Mechanic and S&W357 like this.
  7. S&W357

    S&W357 $upporting Member N.C. WDX-556

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    Yep(y)
     
  8. Dr_DX

    Dr_DX Well-Known Member

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    Apples and Oranges.

    BBI did state that in a video but it wasn't just him. I have talked with other repair shops and that is their opinion as well. The OP was trying to find out what had to be changed to use HG 2879C's in an original Toshiba box. My post was referring to the closest transistor to a "drop in replacement" with NO input and output impedance adjustments in an original Toshiba box was the HG 16D08 version. I still stand by that statement, as do a bunch of repair shops (not builders).

    You are talking about new builds that were never a Toshiba box and where the builder has changed the impedances (from a Toshiba box) to better match the device used.

    That's not what this thread is about.
     
  9. Ranch55

    Ranch55 Sr. Member

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    Those 6-J Toshiba knockoffs are definitely NOT restamped HG's .....
    I have popped the top off of one and compared to a HG, very different construction internally.
    The 6-J knockoffs internally, look pretty much like an original Toshiba 2879. Very robust.

    Now then, the internals of the HG's and DEI's, look identical. Remove the top out of view and you can't tell them apart from one another.
     
    Myst-hic likes this.
  10. RParz

    RParz Member

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    Interesting. I wonder how long until TS burns through their stockpile. I'm thinking of picking up a TS amp but I'd like for it to have HG's in it. That way the pills are easily replaceable in the future without having to rewind the transformers and the like. TS had a reputation of having a decent bias circuit for SSB and for not having any LPF being pretty clean amps when driven clean.
     
    Tokin likes this.
  11. RParz

    RParz Member

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    They all work differently in the amp circuits though, yes? Neither of the above is a drop-in replacement of the other, are they?
     
  12. 144inBama

    144inBama Electricity doesn't kill you, ignorance does.

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    I replaced the DEIs in my TS 500V with Hgs, I made zero changes/mods and the input and output tunes were the same. I actually gained about 50 watts.

    *I did talk to BBI prior and he said there were "very" minor changes you "could" make but were nowhere close to "needed"*
     
    RParz and Shadetree Mechanic like this.
  13. Shockwave

    Shockwave Sr. Member

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    TS has a reputation for having a bias circuit. However, it is a horrible one at that. It lacks in every area from voltage regulation to thermal tracking. It also suffers from RF getting into the bias circuit, the first time you overdrive it and let the smoke out of the 10uh chokes.
     
    144inBama likes this.
  14. RParz

    RParz Member

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    I guess you’re right and I should have been more specific. TS has had this design for decades and the reputation to go with it. I’m sure there’s better ways to do it, but there’s trade offs of diminishing returns. For a mass production item, they’ve always been able to hold their own. For all the types of circuits you’re talking about, there’s plenty of type approved boxes that tick these boxes. With price tags to match.
     
    #29 RParz, Jul 6, 2021
    Last edited: Jul 6, 2021

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